Metal electrodes composed of a valve metal base, such as titanium, tantalum, zirconium, molybdenum, columbium and tungsten, having coatings of mixed metal oxides, especially of metals of the platinum group, have been known for some time (see, e.g., South African Pat. No. 68/7482). Such electrodes, being resistant to attack under electrolysis conditions, are dimensionally stable and permit construction of electrolytic cells having higher capacity and reduced electrical energy requirements. For these reasons, they have found wide use in the production of alkali metal hydroxide and chloride by electrolysis of salt brine. Numerous variations and modifications of dimensionally stable metal electrodes based on such valve metals have been patented or described in the literature. For example, German Offenlegungschrift No. 2,045,348 describes titanium-based metal electrodes having an active coating of a solid solution of titanium dioxide and at least one dioxide of chromium, manganese and/or rhenium. Metal electrodes containing a tellurium-doped conductive coating based on cobalt, chromium, iron, manganese, aluminum, gallium, iridium, rhenium or vanadium, or based on one or more elements of the platinum group, are respectively described in German Offenlegungschrift Nos. 2,136,391 and 2,136,394.
Numerous electrodes for electrochemical reduction of oxygen have been investigated and reported as suitable for use in fuel cells and air batteries. These include MnO.sub.2 -coated electrodes, electrodes having a surface of lithiated nickel oxide, or of mixed oxide films of nickel/praseodymium oxides and nickel/cobalt oxides.
There is always need for new types of metal electrodes for use in electrochemical processes.